A waveguide interface between different function blocks, and between a function block and test equipment, is needed in many situations in microwave technology. Antennas, duplex filters, and amplifiers are examples of such function blocks, and the test equipment may be constituted by any type of suitable measuring or test device.
One of these function blocks is in this context constituted by a so-called substrate integrated waveguide SIW, and there is a need for an enhanced transition from an air-filled waveguide to a SIW. The following properties are found to be of importance:                Mechanically Robust        Lightweight        Low cost        Wide band        Robust to fabrication tolerances        Low loss        Good matching        Millimeter wave range functionality, i.e. for frequencies about 30-300 GHz, in particular 60 and 70/80 GHz.        
Different types of transitions have been made, but none of them have provided a sufficient band width, robustness and low loss, and thus an enhanced transition between a SIW and a waveguide interface is desired.